The invention relates to an apparatus for delivering distance information for a camera, and more particularly, to such apparatus which is capable of deriving the absolute value of distance information for the purpose of driving an automatic focusing device.
As is recognized, an output relating to a distance information of a lens includes both an absolute magnitude and a relative magnitude of distance information. An absolute magnitude of distance information as used in an automatic focusing device refers to a signal which corresponds to the distance itself while a relative magnitude of distance information refers to an offset as referenced to a present distance. Distance information representing a relative distance can be delivered through comb-shaped electrodes alone, for example, which may be advantageously employed in an apparatus for delivering distance information of an interchangeable lens to simplify its construction. However, it is more convenient to use distance information representing an absolute magnitude in a single lens reflex camera which operates as a system camera.
Several means are known for deriving distance information representing an absolute magnitude, including (1) the use of an absolute distance encoder mounted in an interchangeable lens for developing a 4 bit, digital signal of Gray code (see Japanese Laid-Open Patent Application No. 67,650/1975) and (2) the use of a member which is mechanically interlocked with a distance ring of an interchangeable lens and the movement of which is detected by employing a permanent magnet and a magnetoelectric transducer element (see Japanese Laid-Open Patent Application No. 108,828/1985). In either technique, an absolute magnitude of distance is derived in terms of a movement of a lens distance ring converted into an output, that is, by utilizing a member which is directly interlocked with the distance ring.
However, either technique mentioned above requires the provision of an absolute distance encoder or detecting transducer element on every interchangeable lens barrel, and such encoder or element occupies a relatively large space, resulting in an increased size and cost of such lens barrel, which is unfavorable to a user when attempting a systematized use.
The present applicant has previously proposed an apparatus for calculating an absolute distance in which a pulse generator is mounted within an interchangeable lens barrel to develop an address signal which is counted by a CPU (arithmetic and logical unit) also located within the lens for enabling a look-up of a distance code table (see Japanese Patent Application No. 134,800/1985). This apparatus requires a memory for the distance code table.